The forming of can ends or shells for can bodies, namely aluminum or steel cans, is well-known in the art. Shells typically have a center panel connected to an inner panel wall which is connected to a countersink. The countersink is connected to a chuck wall of the shell which is connected to a crown. The crown is connected to a peripheral curl that is structured to be seamed onto a can body.
A problem that exists in prior art tooling assemblies occurs in those situations where an end user has to make an adjustment to the press ram because the heat in the die set causes the tooling to grow which, in turn, causes the shell unit depth to be too deep and out of specification. Oftentimes, the end user has to make a number of press ram adjustments to maintain the shell dimensions at specification until the temperature in the die set stabilizes. These types of adjustments in a high speed shell manufacturing line is both impractical and causes lost production.
In order to eliminate the need for press ram adjustments, a number of end users will adjust the press shutheight to provide a shell unit depth dimension at a low limit of the specification. As the press is stabilized at operating temperatures, the shell will grow in unit depth dimension to a high limit of the specification. Such a practice produces a shell that meets end user specifications, but other processes of the shell manufacturing process is negatively affected, such as, for example, conveying the shells, accumulating the shells and bagging the converted ends. Also, as the product reaches the high limit of the shell unit depth specification, the amount of material in the curl is reduced and this could adversely affect seaming of the final converted can ends onto a can body.
As a press and its associated tooling assemblies reach operating temperatures, expansion of the tooling assemblies change the product dimensions. A die core ring in the lower tooling is coupled to a die retainer coupled to the lower die shoe. The positioning of the die core ring provides for the upper end of the die core ring, which is unrestrained, to axially expand upward. A die center coupled to a die center riser is provided in the upper die shoe. The die center is used to penetrate into the die core ring a fixed distance to provide for a specified shell unit depth. The change in the height of the upper end of the die core ring to a face of the die center causes the shell unit depth of the product to become deeper. This variation in shell unit depth is caused by thermal expansion of the die core ring.
Due to the potentially high internal pressures generated by carbonated beverages, both the can body and the can end are typically required to sustain internal pressures of 90 psi (0.621 MPa) without cracking or deformation. Depending on various environmental conditions such as heat, over fill, high carbon dioxide content, and vibration, the internal pressure in a beverage may exceed internal pressures of 90 psi (0.621 MPa). Recently, shell developments have been focused on engineering various features of the shell including the chuck wall angle in order to reduce the metal content in the shell, but still provide the shell with the capability of sustaining internal pressures exceeding 90 psi (0.621 MPa). Another approach to reducing metal content in the shell is to use reduced gauge metal sheet in the manufacture of the shell. The reduced metal content in the shell makes it desirable for the shells to have dimensions that are centered within the specifications of the end user in order to prevent, for example, rupture and catastrophic failure of the shell. As end users continue to strive to reduce the metal content in shells and improve manufacturing processes, end users desire an apparatus and method for forming shells with a generally uniform depth without the complications of adjusting the press ram, the press shutheight or the like throughout their day-to-day operations.
As a result, a need exists in the art for a shell press and method for forming shells that manufactures shells having a unit depth that centers the dimensions of the shells within the specifications of the end user.
Another need exists in the art for an apparatus and method for forming shells having a uniform unit depth.